1. Technical Field
The present invention relates to ignition of a pyrotechnic transmission line, and is particularly directed to an apparatus including an ignitable pyrotechnic transmission line which, when ignited, actuates a vehicle safety device, such as an airbag inflator, during a vehicle collision.
2. Background Art
The use of an ignitable pyrotechnic transmission line for actuating an airbag inflator is known. The airbag inflator includes ignitable gas-generating propellant grains which are ignited in response to ignition of the pyrotechnic transmission line. Typically, the pyrotechnic transmission line is ignited in response to actuation of a squib which, in turn, is actuated in response to an energy signal from an impact sensor. The impact sensor provides the energy signal when it senses a vehicle collision.
A known igniter for igniting explosives is a semiconductor bridge. One such igniter is disclosed in U.S. Pat. No. 4,708,060 to Bickes, Jr., et al., issued Nov. 24, 1987. The igniter in U.S. Pat. No. 4,708,060 includes a burstable semiconductor bridge which, upon bursting, ignites explosive powder located adjacent to the semiconductor bridge. The semiconductor bridge bursts and ignites the explosive powder when an electrical current of not less than a predetermined magnitude is passed through the semiconductor bridge for at least a predetermined time duration.
Although the igniter in U.S. Pat. No. 4,708,060 is disclosed as being suitable for igniting explosive powder, there is no disclosure in the patent that a pyrotechnic transmission line can be directly ignited by bursting of a semiconductor bridge. An example of a pyrotechnic transmission line is "TLX" (trademark, Explosive Technology, Inc. of Fairfield, California). A TLX pyrotechnic transmission line includes a tube made of a plastic material which can withstand high temperature, such as "KYNAR" (trademark, E. I. DuPont de Nemours & Co. of Wilmington, Delaware) or "HALAR" (trademark, E. I. DuPont de Nemours & Co. of Wilmington, Delaware), on which a reactive coating is disposed. An example of the reactive coating is made of a material including 10.5% aluminum powder and 89.5% "HMX". HMX is cyclotetramethylene-tetranitramine. The velocity of the ignition of a TLX pyrotechnic transmission line is in the range of 5,000-6,000 feet/second.
TLX can be used as an ignitable pyrotechnic transmission line for igniting gas-generating propellant grains in an airbag inflator. TLX is ignited when the reactive coating on the tube is subjected to a pressure pulse of at least a predetermined magnitude for at least a predetermined time duration. There is no disclosure in U.S. Pat. No. 4,708,060 that a semiconductor bridge can be used to provide a pressure pulse of not less than a predetermined magnitude for at least a predetermined time duration to ignite a TLX pyrotechnic transmission line.